Aluminum Anode Alloy

Abstract

The aluminum anode alloy consists essentially of an aluminum base and effective amounts of tin and indium. The aluminum alloy is useful as a sacrificial metallic coating, as a protective aluminum anode, and as a pigment in polymeric coatings.

Description

ORIGIN OF INVENTION[0001]The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.FIELD OF THE INVENTION[0002]The present invention is directed to aluminum alloys and to the use as a protective anode. The aluminum alloys can be used also as a sacrificial metallic coating and as a galvanic pigment in a binder or polymeric protective coating.BACKGROUND OF THE INVENTION[0003]Aluminum anode alloys were initially researched and developed in the 1960's and 1970's. A body of patents and papers were published during this time which detail the exploration of various additive elements to aluminum which would activate it (inhibit the formation of aluminum oxide) and tune the operating potential, or voltage, to match that of pure zinc.[0004]The development of activated aluminum alloys began in the 1960's and intellectual propert...

AI Technical Summary

Benefits of technology

[0006]The present invention relates to compositions of novel aluminum alloys designed to be coupled to materials with a higher operating potential (more positive) and act as a protective anode. The alloy could be used in bulk, applied by various methods as a sacrificial metallic coating, or made into a powder and used as a galvanic pigment in protective coatings such as a pigment in binders or polymeric coatings. The majority of the alloy is aluminum, with very small additions of tin (equal to or less than 0.2% by weight) and indium (equal to or less than 0.05% by weight) added to adjust the operating potential, activity, and efficiency of the alloys.

[0007]The novel feature of this invention is the very small addition of tin which is critical to control operating potential and efficiency. Prior art demonstrates aluminum anode alloys with tin, but higher amounts than the disclosed compositions. In addition, the efficiency of the higher tin alloys is low and thus not attractive for practical applications. Indium is added to stabilize the operating potential and enhance the efficiency of the alloys which would be otherwise lower if only tin were used.

[0008]The alloy compositions described herein are designed to have high operating efficiencies to make the alloy as cost-practical as possible, high current output to enable high and long-lasting performance for a given weight of anode (energy density), and optimized operating potential, which will vary depending on the application. An important added benefit is that the alloys of this invention do not contain zinc. The most used commercial aluminum anode alloy is aluminum-5% zinc-0.02% indium. This alloy is specified in MIL-DTL-24779 and has proven to be very effective in world-wide climates to protect a variety of materials including iron, steel, and aluminum piers, ships, off-shore rigs, and bridges among other applications. It is approximately 90% efficient, which is lower than pure zinc, which is about 98% efficient, but much higher than magnesium, which is about 60% efficient.

Problems solved by technology

In addition, the efficiency of the higher tin alloys is low and thus not attractive for practical applications.

Unfortunately, zinc is an aquatic toxin and contains residual cadmium from the mining process.

Moreover, Zinc is also more expensive than aluminum.

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